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stb_truetype: fix incorrect antialiasing computation in v2 rasterizer, and handle certain cases where math blew up

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This commit is contained in:
Sean Barrett 2021-07-11 16:26:02 -07:00
parent e05ecc05ee
commit 0be82e4814
3 changed files with 52 additions and 16 deletions
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27
stb_truetype.h
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@ -3120,7 +3120,7 @@ static void stbtt__fill_active_edges_new(float *scanline, float *scanline_fill,
scanline_fill[x] += e->direction * height; // everything right of this pixel is filled
} else {
int x,x1,x2;
float y_crossing, step, sign, area;
float y_crossing, y_final, step, sign, area;
// covers 2+ pixels
if (x_top > x_bottom) {
// flip scanline vertically; signed area is the same
@ -3133,28 +3133,39 @@ static void stbtt__fill_active_edges_new(float *scanline, float *scanline_fill,
dy = -dy;
t = x0, x0 = xb, xb = t;
}
assert(dy >= 0);
assert(dx >= 0);
x1 = (int) x_top;
x2 = (int) x_bottom;
// compute intersection with y axis at x1+1
y_crossing = (x1+1 - x0) * dy + y_top;
// if x2 is right at the right edge of x1, y_crossing can blow up, github #1057
if (y_crossing > y_bottom)
y_crossing = y_bottom;
sign = e->direction;
// area of the rectangle covered from y0..y_crossing
area = sign * (y_crossing-sy0);
// area of the triangle (x_top,y0), (x+1,y0), (x+1,y_crossing)
scanline[x1] += area * (1-((x_top - x1)+(x1+1-x1))/2);
scanline[x1] += area * (x1+1 - x_top)/2;
step = sign * dy;
// check if final y_crossing is blown up; no test case for this
y_final = y_crossing + dy * (x2 - (x1+1)); // advance y by number of steps taken below
if (y_final > y_bottom) {
y_final = y_bottom;
dy = (y_final - y_crossing ) / (x2 - (x1+1)); // if denom=0, y_final = y_crossing, so y_final <= y_bottom
}
step = sign * dy * 1; // dy is dy/dx, change in y for every 1 change in x, which is also how much pixel area changes for each step in x
for (x = x1+1; x < x2; ++x) {
scanline[x] += area + step/2;
scanline[x] += area + step/2; // area of parallelogram is step/2
area += step;
}
y_crossing += dy * (x2 - (x1+1));
STBTT_assert(STBTT_fabs(area) <= 1.01f); // accumulated error from area += step unless we round step down
STBTT_assert(STBTT_fabs(area) <= 1.01f);
scanline[x2] += area + sign * (1-((x2-x2)+(x_bottom-x2))/2) * (sy1-y_crossing);
// area of the triangle (x2,y_crossing), (x_bottom,y1), (x2,y1)
scanline[x2] += area + sign * (x_bottom - x2)/2 * (sy1-y_crossing);
scanline_fill[x2] += sign * (sy1-sy0);
}

2
tests/stb.dsp
View File

@ -66,7 +66,7 @@ LINK32=link.exe
# PROP Ignore_Export_Lib 0
# PROP Target_Dir ""
# ADD BASE CPP /nologo /W3 /Gm /GX /ZI /Od /D "WIN32" /D "_DEBUG" /D "_CONSOLE" /D "_MBCS" /YX /FD /GZ /c
# ADD CPP /nologo /MTd /W3 /GX /Zi /Od /I ".." /D "WIN32" /D "_DEBUG" /D "_CONSOLE" /D "_MBCS" /D "DS_TEST" /FR /FD /GZ /c
# ADD CPP /nologo /MTd /W3 /GX /Zi /Od /I ".." /D "WIN32" /D "_DEBUG" /D "_CONSOLE" /D "_MBCS" /D "TT_TEST" /FR /FD /GZ /c
# SUBTRACT CPP /YX
# ADD BASE RSC /l 0x409 /d "_DEBUG"
# ADD RSC /l 0x409 /d "_DEBUG"

39
tests/test_truetype.c
View File

@ -37,7 +37,7 @@ int main(int argc, char **argv)
{
stbtt_fontinfo font;
unsigned char *bitmap;
int w,h,i,j,c = (argc > 1 ? atoi(argv[1]) : 34807), s = (argc > 2 ? atoi(argv[2]) : 32);
int w,h,i,j,c = (argc > 1 ? atoi(argv[1]) : '@'), s = (argc > 2 ? atoi(argv[2]) : 32);
//debug();
@ -49,6 +49,25 @@ int main(int argc, char **argv)
stbtt_InitFont(&font, ttf_buffer, stbtt_GetFontOffsetForIndex(ttf_buffer,0));
#if 0
{
stbtt__bitmap b;
stbtt__point p[2];
int wcount[2] = { 2,0 };
p[0].x = 0.2f;
p[0].y = 0.3f;
p[1].x = 3.8f;
p[1].y = 0.8f;
b.w = 16;
b.h = 2;
b.stride = 16;
b.pixels = malloc(b.w*b.h);
stbtt__rasterize(&b, p, wcount, 1, 1, 1, 0, 0, 0, 0, 0, NULL);
for (i=0; i < 8; ++i)
printf("%f\n", b.pixels[i]/255.0);
}
#endif
#if 1
{
static stbtt_pack_context pc;
static stbtt_packedchar cd[256];
@ -60,16 +79,14 @@ int main(int argc, char **argv)
}
#endif
#if 1
{
static stbtt_pack_context pc;
static stbtt_packedchar cd[256];
static unsigned char atlas[1024*1024];
unsigned char *data;
stbtt_PackBegin(&pc, atlas, 1024,1024,1024,1,NULL);
stbtt_PackFontRange(&pc, ttf_buffer, 0, 32.0, 'u', 1, cd);
stbtt_PackEnd(&pc);
data = stbtt_GetCodepointSDF(&font, stbtt_ScaleForPixelHeight(&font,32.0), 'u', 4, 128, 128/4, &w,&h,&i,&j);
for (j=0; j < h; ++j) {
for (i=0; i < w; ++i) {
@ -77,8 +94,8 @@ int main(int argc, char **argv)
}
putchar('\n');
}
return 0;
}
#endif
#if 0
stbtt_BakeFontBitmap(ttf_buffer,stbtt_GetFontOffsetForIndex(ttf_buffer,0), 40.0, temp_bitmap[0],BITMAP_W,BITMAP_H, 32,96, cdata); // no guarantee this fits!
@ -117,8 +134,16 @@ int main(int argc, char **argv)
return 0;
#endif
bitmap = stbtt_GetCodepointBitmap(&font, 0,stbtt_ScaleForPixelHeight(&font, (float)s), c, &w, &h, 0,0);
(void)stbtt_GetCodepointBitmapSubpixel(&font,
0.4972374737262726f,
0.4986416995525360f,
0.2391788959503174f,
0.1752119064331055f,
'd',
&w, &h,
0,0);
bitmap = stbtt_GetCodepointBitmap(&font, 0,stbtt_ScaleForPixelHeight(&font, (float)s), c, &w, &h, 0,0);
for (j=0; j < h; ++j) {
for (i=0; i < w; ++i)
putchar(" .:ioVM@"[bitmap[j*w+i]>>5]);